The present invention relates to a method for the in-situ synthesis and screening of tetra-arylporphyrins, meso-octamethyl calix(4)pyrroles and allied macrocycles by reacting pyrrole and corresponding aldehydes and ketones using a specific zeolite based molecular sieve catalyst as sorbent in thin layer chromatography under microwave irradiation. In particular, the present invention provides new opportunities for parallel synthesis and screening on a single plate for producing tetraphenyl porphyrins by reacting pyrrole with benzaldehyde and calix(4)pyrroles from pyrrole and acetone in presence of zeolites and MCM-41 molecular sieves as sorbents in TLC under microwave irradiation with an online spectroscopic evidence.
The process of the invention leads to efficient and quantitative method for the screening of the selective catalytic activity of a zeolite catalyst as sorbents in TLC for in-situ synthesis of tetraaryl porphyrins, calix(4)pyrroles and allied macrocycles. The zeolite based TLC plays the role of a microreactor cum separator exemplified by rapid processing for possible applications to combinatorial chemistry.
In recent years, significant effort has been directed towards the design and synthesis of macrocycles such as porphyrins and calix(4)pyrroles over mesoporous molecular sieves. Among the various macrocycles, extensive research in the area of synthesis, characterization and utilization of porphyrins and calixpyrroles is in progress. Synthesis of Porphyrin and Calix(4)pyrrole compounds as well as methods for synthesising the same are well recognised in the art. Porphyrins are conjugated macrocyclic species composed of four pyrrole rings linked to the position via sp2 hybridized carbon atoms. However porphyrin and pyrrole compounds are expensive. For example, porphyrin is offered at costs as high as $15,000/g. Even though a great variety of catalysts like organic and inorganic acid catalysed syntheses are reported they suffer from the reusability of the catalyst and poor yields. Further, the impure corroles formation makes the separation of the pure compound difficult. The first such report of synthesis of porphyrin molecules under microwave irradiation by A. Petit et al (Synthetic Communication 22(8) (1992) 1139) by employing silica alumina, clay and montmorillonite as a catalyst is popular but it suffers from poor yields (not more than 10%).
Calix(4)pyrroles represent a class of macrocycles, which are non-conjugated macrocyclic species composed of four pyrrole rings linked to the position via sp3 hybridized carbon atoms. Calixpyrroles that carry meso-hydrogen atoms are prone to oxidation to the corresponding porphyrins. Recently we have reported the synthesis of these Calix(4)pyrroles over zeolites and mesoporous MCM-41 molecular sieves with good yields and selectivities, which is an eco-friendly and environmentally clean process (Chem. Commun. 2001, 2226). Such macrocycles have unusual properties that make them particularly useful. Calixpyrroles bind anion and neutral molecular species in solution and in the solid state in such an effective and selective way the anions or neutral molecular species can be separated from other anions and neutral molecular species. Further the affinity a macrocycle has for a particular species can be xe2x80x98tunedxe2x80x99 by strategic choice of electron-donating or electron-withdrawing peripheral substituents for the synthesis of macrocycles.
According to WO 97/37995, various types of calixpyrroles was synthesized using different ketones. Application of these macrocycles for removal of biological ions or neutral molecule species for clinical use, removal of undesirable ions or neutral molecule species from environmental sources provides only a few of the practical and important uses. These calix(4)pyrroles can be used in the dialysis of bodily fluids. Examples of dialyzable substrutex include, but are not limited to phosphate containing molecules or halide waste (i.e. diabetes or drug overdoses and kidney dialysis).
Since these macrocycles, viz., porphyrins and calix(4)pyrroles are important moieties in host-guest chemistry as drug transporting agents, their synthesis demands an eco-friendly, clean, economical and free handling process.
Porous materials created by nature or by synthesis have found great utility in all aspects of human activity. The pore structure of solids is usually formed in the stages of crystallization or subsequent treatment. Depending on their predominant pore size, the solid materials are classified as microporous, mesoporous and macroporous materials. The only class of porous materials possessing rigorously uniform pore sizes is that of Zeolites and related molecular sieves. Zeolites are uniform porous crystalline aluminosilicates and their lattice is composed by TO4 tetrahedra (T=Al and Si) linked by sharing the apical oxygen atoms (D. W. Breck, Zeolite molecular sieves: Structure, Chemistry and Use; Wiley and Sons; London 1974). But due to the smaller pore size of zeolite molecular sieves restricted their wide range applications, especially in synthesis of macrocycles. However, this has been overcome by the report of Mesoporous molecular sieves by Mobil researchers (C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli and J. S. Beck, Nature 359 (1992) 710) in 1992. These Mesoporous molecular sieve (MCM-41) has been opened a new era in the zeolite catalysis. Many reports have been published on the applications of this material for the catalytic activity towards oxidation, acylation, alkylation and cyclization. They are the support materials for enzymes, whole cell immobilization and nano particles. Their potentiality, due to organized pore structure with large surface area, has stimulated research in different fields of application among which catalysis, adsorption and chromatography are the most interesting ones. The first usage of mesoporous silica and aluminosilicate as stationary phases was reported by Grun et al, which prepared MCM-41 material in alkaline medium from cationic surfactants (J. Chromatography A 740, 1, 1996). Recent reports utilized the technique of silica gel thin layer chromatography (TLC) and microwave irradiation as a tool for reaction optimization. (Chem. Commun 2000, 435; Tetrahedron Letters 42, 2001, 3913). However, the method is limited to synthesis of simple molecules.
The main object of the present invention is to provide a process for the in-situ synthesis and evaluation of porphyrins such as meso-tetraphenyl porphyrin over zeolite and MCM-41 molecular sieves coated TLC plates under microwave conditions, where in a fast, eco-friendly heterogeneous catalytic process could be accomplished.
Another object of the present invention is to provide a process for the in-situ synthesis and evolution of calix(4)pyrroles such as meso-octamethyl calix(4)pyrrole over zeolite and MCM-41 molecular sieves coated TLC plates under microwave conditions, where in a fast, eco-friendly heterogeneous catalytic process could be accomplished.
Still another object of the present invention is in-situ synthesis of porphyrins, calix(4)pyrroles and allied macrocycles over molecular sieves coated TLC plates with microwave assisted reaction.
The present invention relates to a the use of zeolites and mesoporous MCM-41 as stationary phases in TLC, for a rapid, in-situ synthesis, identification and quantification of Porphyrins, Calix(4)pyrroles and allied macrocycles using the combinatorial approach to identify and estimate the yield of product. The present invention provides an in-situ synthesis of porphyrins and calix(4)pyrrole compounds and their simultaneous screening over solid acid catalysts. It provides new opportunities for the combinatorial approach for the rapid screening of macrocycles.
Accordingly, the present invention provides a method for high performance. Thin Layer Chromatography (TLC) and microwave assisted in-situ synthesis and evaluation of a tetraphenyl porphyrin comprising reacting the corresponding pyrrole and an aromatic aldehyde, on a glass backed zeolite catalyst coated TLC plate.
In one embodiment of the invention, the zeolite is coated onto the TLC plate using a binder selected from the group consisting of calcium sulfate, gypsum, starch and cellulose.
In another embodiment of the invention, the catalyst used is selected from the group consisting of Al-MCM-41, HZSM-5, Hxcex2, HX, synthetically prepared SAPO-5 and HY.
In another embodiment of the invention, the zeolite used is in its alkali ion form wherein the alkali ion is selected from the group comprising sodium and potassium, ammonium ion form or proton form.
In another embodiment of the invention, the aromatic aldehyde is selected from the group consisting of benzaldehyde, o, m and p-substituted benzaldehydes.
In another embodiment of the invention, the process comprises the in situ synthesis and characterization of meso-tetraphenyl porphyrin of formula 1 
from corresponding pyrrole and benzaldehyde over mesoporous and microporous molecular sieves as stationary phases on inert glass backed supports in solvent free microwave heating.
The present invention also relates to a method for the high performance Thin Layer Chromatography (TLC) and microwave assisted in-situ synthesis and evaluation of meso-octamethyl calix(4)pyrrole comprising reacting the corresponding pyrrole and ketone over a glass backed zeolite coated TLC plate.
In one embodiment of the invention, the catalyst used is selected from the group consisting of Al-MCM-41, HZSM-5, Hxcex2, HX, synthetically prepared SAPO-5 and HY.
In another embodiment of the invention, the ketone is selected from the group consisting of acetone, methyl ethyl ketone, diethyl ketone, cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone, cyclododecanone, substituted cyclohexanones, acetophenone and alkyl and aryl derivatives thereof.
In one embodiment of the invention, the zeolite is coated onto the TLC plate using a binder selected from the group consisting of calcium sulfate, gypsum starch and cellulose.
In another embodiment of the invention, the zeolite used is in its alkali ion form wherein the alkali ion is selected from the group comprising sodium and potassium, ammonium ion form or proton form.
In another embodiment of the invention, the process comprises the facile and in situ synthesis of a meso-octamethyl calix(4)pyrrole of the formula 2 
from the corresponding pyrrole and acetone over mesoporous and microporous molecular sieves as stationary phases on inert glass backed supports in solvent free microwave heating.